Calculation of the amount of disk space required for recording and storing video images received from IP video cameras.
Creating a video surveillance system based on an IP network requires not only knowledge of network technologies and competent network segmentation with traffic calculation, but also planning the system archive.
Of course, it is important to calculate the amount of disk space for archiving devices. This is especially relevant given the modern requirements for network video surveillance systems — transmission and recording with a characteristic of 25 frames per second for each IP camera. This primarily concerns medium and large systems, where the number of channels is more than 80-100. In such systems, an error in calculation can lead to significant additional costs associated not only with the purchase of additional hard drives, but also network video recorders or storage devices.
As a rule, manufacturers of network video surveillance systems provide detailed information and clear recommendations for calculating the archive. Detailed calculation formulas can be found in the documentation. However, the installer often has to improvise based on the customer's preferences regarding different brands of IP cameras. In this case, it is necessary to know the exact parameters and characteristics of the video traffic.
At first glance, the calculation is relatively simple. The following formula expresses the volume of recorded information per hour in GB from one camera: Q = 0.45 x U, where U is the video traffic from one camera in Mbit/sec.
The value of video traffic transmitted by an IP camera can be found in the device passport. Each manufacturer specifies this parameter. However, it is recommended to check, since the passport value and real data may differ significantly. The reason is not the desire of the IP camera manufacturer to embellish reality, but the objective complexity of determining this parameter. Due to the fact that IP cameras use so-called hybrid compression algorithms (MPEG, H.26x) for image compression, using intra-frame and inter-frame compression techniques, the traffic is not constant. For static scenes, video traffic is several times less than for dynamic ones. Usually, manufacturers specify either the maximum traffic or some average value, the so-called typical.
However, independent verification is more preferable. Especially if any limits are set, for example, recording at a certain speed and resolution. To measure traffic, you can use the camera connection to a personal computer. Using the «network» tab in the Windows task manager, you can find out the video traffic from the IP camera. It is important to simulate scenes that may be present at a real facility and estimate the traffic values. The actual volume of recorded information will be lower, since the traffic also includes service information.
In the case of recording by a video detector or sensor, it is necessary to take into account the reduction factor that takes into account the activity at the facility and the number of alarms, as well as the recording parameters (before and after the alarm). Knowing the volume of information from each camera, all that remains is to add these values to calculate the archive capacity for the entire system.